Process for the production of tetraalkyl lead

ABSTRACT

PRODUCTION OF TETRAALKYL LEAD BY REACTION OF ALKYL HALIDE WITH LEAD-SODIUM ALLOY IN POLAR APROTIC SOLVENTS SUCH AS TETRAHYDROFURAN AND DIMETHYL FORMANIDE. THE TEMPERATURE OF REACTION RANGES FROM 20-60*C., THE PRESSURE RANGES FROM 1-2 ATM. AND THE RATIO OF ALKYL HALIDE TO ALLOY IS 1:1. THE SOLVENT AND FINAL PRODUCT ARE DISTILLED OFF IN A VACUUM IN A STREAM OF NITROGEN.

United States Patent 3,647,844 PROCESS FOR THE PRODUCTION OF TETRAALKYL LEAD Nikolai Vasilievich Komarov, Ulitsa Lemontova 315, kv. 32, and Tatyana Ivanovna Ermolova, Ulitsa Bograda 1, kv. 22, both of Irkutsk, U.S.S.R. N0 Drawing. Filed July 29, 1969, Ser. No. 845,873 Int. Cl. C071? 7/24 US. Cl. 260-437 R 6 Claims ABSTRACT OF THE DISCLOSURE Production of tetraalkyl lead by reaction of alkyl halide with lead-sodium alloy in polar aprotic solvents such as tetrahydrofuran and dimethyl formamide. The temperature of reaction ranges from -60 C., the pressure ranges from 1-2 atm. and the ratio of alkyl halide to alloy is 1:1. The solvent and final product are distilled off in a vacuum in a stream of nitrogen.

The present invention relates to processes for the production of tetraalkyl lead, which is widely employed as an antiknock agent for motor fuels.

Processes for the production of tetraalkyl lead are known wherein monochloro-, bromoor iodoalkyl is reacted with a lead-sodium alloy consisting of 90 wt. percent lead, 9.5-9.8 wt. percent sodium and 0.2-0.5 wt. percent potassium at a temperature of 50160 C., a pressure of 85-19 atm. and molar ratio of alklyl halide to alloy from 6:1 to :1 in the presence of activators and thermostabilizers, followed by steam distillation of the final product.

A disadvantage of such prior art said known processes is that they are carried out at high temperature and pressure which makes it necessary to use special equipment.

Another disadvantage thereof is that during steam distillation of the final product a large amount of efiiuents are produced which are contaminated with tetraalkyl lead and require special purification installations.

Moreover, therefor previously known methods require the use of activators and thermostabilizers.

Still another disadvantage of the foregoing prior art techniques is the caking of the slurry formed, which comprises a mixture of lead and sodium chloride.

These processes also require a large excess of alkyl halides and a lengthy period of time for their completion (3-8 hours).

It is an object of the present invention to eliminate the above disadvantages.

It is a further and more specific object of the invention to provide a simpler and more efiicient process for the production of tetraalkyl lead which is carried out at lower temperature and pressure and requires less time, and wherein no excess of alkyl halides is used, no contaminated efiluents are formed, there is no caking of slurry and special activators and thermostabilizers are not employed.

The foregoing objects have been achieved by the provision of a process for the production of tetraalkyl lead involving the reaction of monochloro, bromoor iodoalkyl with a lead-sodium alloy consisting of 90' wt. percent lead, 9'.5-9.8 wt. percent sodium and 0.2-0.5 wt. percent potassium, followed by distillation of the final product, wherein, according to the invention, the reaction is carried out in tetrahydrofuran or dimethylformamide at a temperature of 20-60 C., a pressure of 1-2 atm. and a molar ratio of alkyl halide to lead-sodium alloy of 1:1, and said solvents and final product are distilled off in vacuum in a stream of nitrogen.

Carrying out the synthesis in tetrahydrofuran or dimethformamide makes it possible to substantially intensify the process.

The present process is economical and safe, and is easily carried out on an industrial scale. The process is outstanding for its simplicity from the engineering standpoint and in the plant employed; it provides a yield of up to 91% of theory.

The present process is carried out as described hereinbelow.

To lead-sodium alloy of the composition specified above and prepared by the conventional method, charged to a reactor with tetrahydrofuran or dimethyl formamide, there is added with stirring at a temperature of 20 C. and under atmospheric pressure an alkyl halide, maintaining the temperature of the reaction mixture not higher than 60 C., the reaction being exothermic. If the system is closed the pressure may rise to 2 atm. The reaction continues for 0.5-3 hr. with constant stirring. The solvent and product are then distilled oil in a stream of nitrogen. The tetrahydrofuran or dimethylformamide recovered is recycled without additional purification. The remaining free-flowing mass comprising a mixture of finely dispersed lead and sodium chloride is utilized for preparing the lead-sodium alloy.

The process of the present invention is illustrated in the following examples.

EXAMPLE 1 Into a flask fitted with a mechanical stirrer, a Vigreux column (or reflux condenser), a thermometer and a gas delivery tube are placed 77 g. of lead-sodium alloy consisting of 90 wt. percent lead, 9.5 Wt. percent sodium and 0.5 wt. percent potassium, and 60 ml. (52 g.) of tetrahydrofuran. To the mixture is then added at atmospheric pressure and with stirring 26 g. of ethyl chloride in small portions during 3 hours, the temperature of the reaction mixture rising to 55 C.

On completion of the reaction the solvent is distilled oil in a stream of nitrogen at room temperature under reduced pressure of 50 mm. of mercury. 51 g. of tetrahydrofuran is recovered.

Tetraethyl lead is then distilled at 60 C./4.5 mm. There is obtained 22 g. of the final product on the basis of sodium); B.P. 60 C./4.5 mm.; n 1.5185.

After the tetraethyl lead has been distilled there re mains in the flask a dry, grey, free-flowing mass that does not react with water and comprises a mixture of finely dispersed lead and sodium chloride which is suitable for the preparation of a fresh batch of lead-sodium alloy.

EXAMPLE 2 Into a flask are placed 77 g. of lead-sodium alloy of the composition specified in Example 1 and 50 ml. (44 g.) of tetrahydrofuran, and 44 g. of ethyl bromide is added with stirring over a period of 2 hours, during which time the temperature of the reaction mixture rises to -50 C.

In the conditions described in Example 1 there are recovered 40 g. of tetrahydrofuran and 20 g. of tetraethyl lead (77% on the basis of sodium).

EXAMPLE 3 The synthesis is carried out in a pilot plant.

A reactor is charged with 20 kg. of lead-sodium alloy of the composition specified in Example 1 and 10 l. of tetrahydrofuran. The reactor is hermetically closed and the entire system blown out with nitrogen. The stirrer and condenser are turned on and the mixture warmed to 30 C. by letting hot water into the jacket. 1 l. of ethyl 

